Using my laptop vs my desktop to watch movies or listen to music, etc there is an obvious difference in overall sound quality when you take into account ambient noise (i.e. speakers). The difference between -100db noise floor and -110db noise floor for 24 bit audio doesn't come into play if you have an extra 10-15 db ambient noise. Which means if you go for a quality PCI card, you best make sure the PC is up to par in being dead (or at least almost) silent. Otherwise it'd be like going to a theater with absolutely awesome acoustics only to sit next to some jerk who answers his cell phone.
I like the external power supply. It allows you flexibility to isolate power supply or ground noise. Note however that by virtue of being an external USB device with external PSU, it does not automatically imply isolation from the PC's noise (as some usb audio marketing like to claim) because the ground can still be carried through USB cable via the power pins. I see posts complaining about usb audio 'noises' following computer activity that I am betting is because of ground issues. And I don't doubt that if ground noise is carried through the co-axial digital output, the result is suboptimal, but the short and skinny of it is that it depends on your completed setup. You can easily modify cheap usb cable and perform a 'ground lift' that way if you need to. With an internal card you can be more at mercy to the computers grounding and psu design (and a simple loopback test won't show anything there since there is only one ground reference in that test as opposed to the possibility of more in a completed setup). Optical to DAC also avoids this. Course I suppose you can always use cheater plugs all around, but I'd feel better ground lifting a usb cable to a cheap USB audiophile vs the mains power plug to an expensive DAC or amp.
I think the USB audiophile is probably the cheapest one that gets usb audio (mostly) right. It also doesn't crack and pop like cheaper solutions can (since you can adjust latency), and has enough fidelity to at least get 16-bit done right (which sadly even in this day and age can still be rare), and finally digital outputs when you want to go further. Properly setup with no ground issues, I can amplify the output to max on pretty much any amp I've owned(an 11 gain M3 or Grace901 being some of the loudest) with sensitive headphones without having *any* audible noise floor. I've measured 100+ in S/N and dynamic range going through the gilmore lite which is plenty good for me and far better than a *lot* of consumer audio priced at $99. When you pine for something better, it can easily be relegated to a secondary system or use at work or whatever since usb ports aren't hard to come by.
